1. Field of the Invention
The present invention relates to an analysis system which comprises an automatic sample feeding apparatus for selecting a sample to be analyzed (i.e., target sample) from a plurality of prepared samples, or changing a target sample, such as an automatic sampler or an automatic sample changer, and an optical measuring apparatus including a light detection device, such as a photodiode array detector. The analysis system of the present invention is suitable for a high performance liquid chromatograph or the like.
2. Description of the Related Art
A multi-channel spectrophotometer using a photodiode array detector as a light detection device is designed such that light having a given wavelength band is emitted to a sample, and wavelengths of transmitted light which has undergone absorption during passing of the emitted light through the sample are spectrally dispersed by a spectral dispersion device, such as a diffraction grating, whereafter an intensity of the light with the wide wavelength is concurrently detected by the photodiode array detector. This type of spectrophotometer is capable of measuring an absorption spectrum in a given wavelength band without mechanically rotating the diffraction grating. Therefore, it is commonly used as a light detection device of a high performance liquid chromatograph (HPLC), etc., as well as being used by itself.
In the above photodiode array (PDA) detector or a single-photodiode detector, a dark current flows even in a state when no light is entered into a light-receiving element (photodiode), to cause noise in measurement. As one countermeasure against this problem, before acquiring data reflecting light absorption of an intended sample, data about a dark current is acquired to perform a processing of correcting actual absorption data based on the acquired dark current data. As for an operation of measuring a dark current, there has been known a technique of arranging on a light path a shutter adapted to be selectively opened and closed in a mechanical manner, and measuring a dark current under a condition that the shutter is closed to block off light to be entered into the PDA detector, as disclosed, for example, the following Patent Document 1.
In a conventional HPLC equipped with the above multi-channel spectrophotometer using a photodiode array detector as a light detection device, the shutter is closed at the time of start of analysis, i.e., just after a sample is injected into a mobile phase to be fed to a column, so as to measure a dark current, and then opened after completion of the operation of measuring the dark current, so as to start acquiring absorption data of an eluate from the column, as disclosed in the following Patent Document 2. The shutter involves mechanical open and close movements, and it typically takes about 6 to 7 seconds as a dark-current measurement time required for completing the series of operations, i.e., closing the shutter→measuring the dark current→opening the shutter, after a command to measure a dark current is issued from a CPU. Generally, in the conventional HPLC, a time period from injection of a sample into the mobile phase through until a component of the sample is initially eluted from an outlet end of the column, is sufficiently greater than the dark-current measurement time.
Recent years, in connection with development of chromatography techniques primarily intended to provide enhanced throughput, a time period from injection of a sample into a mobile phase through until a component of the sample reaches a light detection device, has been drastically reduced. In some cases, it takes less than 10 seconds before a sample component is initially eluted off of a column. Thus, if the above conventional measurement technique is employed in such a multi-channel spectrophotometer, a part of sample components are likely to reach a light detection device before the operation of measuring a dark current is completed to establish a state capable of acquiring absorption data, which results in the preclusion of detection of the part of sample components.                [Patent Document 1] JP 08-122150A (paragraphs [0002] to [0005])        [Patent Document 2] JP 11-118781A (paragraph [0003])        